Various methods for manufacturing an inorganic oxide that contains a medium-sized pores or mesopores are known. In general, a micropore is defined as a pore having a diameter of less than 2 nm, ae mesopore is defined as a pore having a diameter of from 2 nm to 50 nm, and a macropore is defined as a pore having a diameter of greater than 50 nm. Inorganic oxides can be used as a catalyst, a catalyst auxiliary, or an adsorbent. In addition, inorganic oxides may be combined with zeolite.
Alkali metal-based oxides or alkaline earth metal-based oxides that are typical examples of such inorganic oxides have been in the spotlight as an absorbent for capture and storage of carbon dioxide. In recent years, metal oxide nanoparticles are widely used in an adsorbent, a catalyst, a sensor, and the like since they have a high ratio of surface area to volume. Among them, MgO is considered as a promising catalyst and a promising adsorbent for environmental contaminants.
MgO reacts with CO2 to be converted into MgCO3. However, a low ratio of surface area to volume and the carbonate layer formed on the surface are a barrier when an alkaline earth metal-oxide such as MgO undergoes an additional reaction with CO2. Hence, a measure for increasing the adsorption efficiency of an alkali metal-based or alkaline earth metal-based CO2 adsorbent is required.
As an effective method for increasing the CO2 adsorption efficiency of an alkali metal-based or alkaline earth metal-based oxide, there is a method to expose more active sites by decreasing the particle size.
From this point of view, a method for manufacturing a nanostructure of magnesium oxide is disclosed in Non-Patent Document 1. According to this method, magnesium acetate tetrahydrate as the metal source, ammonium oxalate monohydrate as the capping ligand, and a surface active agent are mixed, heated for 24 hours at 40° C., and then aged for 100 hours at 80° C. Thereafter, the mixture is filtered, washed, dried, and then sintered for 4 hours at 850° C., thereby synthesizing a porous MgO nanostructure having a specific surface area of 47 m2g−1 and a pore diameter of 24 nm.
According to the method of Non-Patent Document 1, a mesoporous material is manufactured through a multi-step reaction, thus the manufacturing process is complicated and requires a long period of time of about one week, and the mass production is difficult, the surface active agent and the like that are used generate secondary environmental contaminants, and it is economically infeasible. In addition, the specific surface area or the pore diameter falls short of the expected level.
Hence, it is urgent to supply an inorganic oxide which saves energy by being manufactured as a mesoporous inorganic oxide at a relatively low temperature, is economically feasible as the manufacturing process is simplified, is environmentally friendly, and leads to an optimized efficiency in an adsorbent, a catalyst, a sensor, and the like as a process for mass production is developed.